L.D.
Wow, that's very nice of you to step in and help your nephew out like that. Your nephew is almost an adult so, when he turns 18, he will be able to make the decision of where he wants to live without any interferance from his parents (hopefully). And he is old enough now to go out and get a part-time job to make a little extra money to help offset expenses as long as it does not interfere with him completing high school. I really wouldn't hold out any hope that his parents will help you and their son financially because it sounds like they are pretty messed up but there are charitable organizations out there that can probably help your son get the school supplies he needs. I don't know if you have a Catholic Charities out where you live but maybe you can contact them to see what kind of assistance they can help you out with. And maybe one of the counselors at your son's new school can help you access some services to help him out until he is ready to graduate.
Wish I could be of more help. God Bless.